I've forgotten which controller has temp comp, that is inexpensive, but others here on the Forum have used it. My Morningstar MPPT-15 does a brilliant job with temp comp but it may be out of your budget limits.
If you get a controller that doesn't have temp comp, it may be all that is necessary for a 6 month storage situation. If the batteries are in Montana at, say, Sept. and you wish to charge them until Apr., select a float voltage that is just a wee bit more than typical. Your batteries should manage fine.
